1. Field of the Invention
The present invention relates to an abnormality determination device and an abnormality determination method for an internal combustion engine, and more particularly to a technique to determine if the fuel injection timing is abnormal.
2. Description of the Related Art
Internal combustion engines in which fuel is injected from an injector, such as diesel engines, are known. Internal combustion engines (in particular, diesel engines) output torque according to the fuel injection timing from the injector. That is, the fuel injection timing significantly influences the output torque. Thus, the desired torque is not output if the fuel injection timing is abnormal. Therefore, it is desirable to determine if the fuel injection timing is abnormal using an on-board diagnostic system (OBD).
Japanese Patent Application Publication No. 5-187300 (JP-A-5-187300) discloses an malfunction cause determination device for a fuel device that can determine the cause of a failure when an error has occurred in fuel injection timing control. The malfunction cause determination device disclosed in JP-A-5-187300 includes: a target injection timing calculation section that calculates the target fuel injection timing supplied from a fuel injection pump to an internal combustion engine according to the operating state of the internal combustion engine; an actual injection timing detection section that detects the actual fuel injection timing of the internal combustion engine; a fuel injection timing control section that performs feedback control so as to match the actual injection timing to the target injection timing; an malfunction determination section that compares the actual injection timing and the target injection timing to determine that a malfunction has occurred if the deviation between the injection timings is out of a predetermined range; and a determination section that determines whether the variation band of the actual injection timing is in a predetermined range when the malfunction determination section has determined a malfunction, to determine a failure of the fuel injection pump if the variation band of the actual injection timing is in the predetermined range.
In the malfunction cause determination device described in this publication, the malfunction determination section determines whether the deviation between the actual fuel injection timing and the target fuel injection timing falls within a predetermined range, and if the malfunction determination section determines a malfunction, the determination section determines whether the variation band of the actual injection timing falls within a predetermined range to determine that a failure of the fuel injection pump has occurred if the variation band of the actual injection timing falls within the predetermined range.
In the malfunction cause determination device described in JP-A-5-187300, a malfunction is determined according to the difference between the actual injection timing and the target injection timing. Therefore, it is difficult to determine whether there is a malfunction unless the target injection timing is constant. However, the target injection timing is often difficult to keep constant during operation of the internal combustion engine. Therefore, there has been room for further improvement to precisely determine a malfunction.